1. Field of the Invention
The present invention relates to a pulley structure of a belt type continuously variable transmission and a method of coupling its moving sheave with a hydraulic actuator member thereof.
2. Prior Art
A belt type continuously variable transmission comprises a primary (driving) shaft, a secondary (driven) shaft provided in parallel with the primary shaft, a primary pulley fixed on the primary shaft, a secondary pulley mounted on the secondary shaft and a driving belt looped over both pulleys, thereby the speed of the secondary shaft can be varied continuously by changing a ratio of running diameters between both pulleys. The ratio of running diameters is changed by regulating a groove width of the both pulleys respectively.
In this type of the continuously variable transmission, as shown in FIG. 6, one pulley assembly, for example, the primary pulley comprises a shaft 11, a stationary sheave 10 rigidly mounted on the shaft 11, a boss 21 coaxially coupled with the shaft 11 so as to be axially displaceable thereon, a moving sheave 20 rigidly mounted on the boss 21, a plurality of ball grooves 11a and 21a provided on the shaft 11 and boss 21 respectively and balls provided between ball grooves 11a and 21a so as to displace the boss 21 along the shaft 11 smoothly. Thus, a groove is formed between the stationary sheave 10 and the moving sheave 20.
The groove width L is controlled by a hydraulic actuator 30 which comprises a piston 31 fixed to the moving sheave 20 at the back side thereof and a cylinder 35 connected with the stationary sheave 10. When hydraulic fluid is supplied to the hydraulic actuator 30, the moving sheave 20 is slid on the shaft 11 of the stationary sheave 10 by the hydraulic actuator 30 so as to regulate the groove width L.
Because of this, it is necessary to secure a strong connecting structure with adequate pressure proof between the moving sheave 20 and the piston 31. Japanese Utility Model Application Laid-open No. Jitsu-Kai-Hei 3-114657 discloses a technique in which, as shown in FIGS. 7 and 8, an end portion of the piston 31 is caulked into an annular groove 23 provided on the back face of the moving sheave 20 so as to rigidly connect the piston 31 with the moving sheave 20.
Further, Japanese Examined Patent Application No. Toku-Ko-Hei 4-79733 discloses a method in which a roller is pressed on the outer periphery surface of the piston while the piston is being rotated integrally with the moving sheave so as to apply a caulking connection between the piston and the moving sheave.
Generally, the connecting strength between the moving sheave 20 and the piston 31 is proportional to the contact area between the annular groove 23 formed on the back face of the moving sheave 20 and the caulking portion of the piston 31. However, according to this prior art, the plastic flow portion of the end of the piston 31 has a U-shaped cross section as illustrated in FIG. 9 and consequently a sufficient contact area can not be obtained between the annular groove 23 and the piston 31. On the other hand, when a greater force is applied to a roller 45 in order to enlarge the contact area by increasing the amount of caulking, the end portion 31a of the piston 31 is excessively deformed and finally exceeds a plastic limit, leading to a production of cracks and furrowings therein. The cracks and furrowings cause not only a lack of strength but also a leakage of hydraulic fluid from inside of the hydraulic actuator 30.